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Terrence writes:
<<Have you researched accidetn data (like I did)
and found that the airlines report safety in terms of passesnger
miles? Is a 747 with 500 passengers 500 times safer than one with
jujst crew? And since that's abviously a lying statistic, >>
Don't you just love statistics. Of the "lower" branches of mathematics
it is one of the least understood, and consequently, most abused. For
example, it is statistically accurate to say that everyone in the
United States has slightly less than one testicle. The average is
skewed from a whole number by the slightly higher population of
females, and not because of Lance Armstrong.
Likewise, Terrence's statistical argument may be accurate (which it
does not seem to be for 2004 data) but it is not relevant. His is
taking the actuary's perspective where the insurance company is
insuring the entire airframe and the actuary must compute the death per
flight hour coefficient in order to determine the insurance premium.
This is a risk calculation, not a personal safety calculation. For the
calculation to have relevance to you it must be expressed in
terms of your probability of being one of the fatalities.
As an individual I only care about my personal risk in evaluating
safety. How many hours do I need to fly before death is a near
certainty. If I happen to be the sole occupant or one of 200 passengers
it is irrelevant as I am just as dead, not 1/200 or 200 times as dead,
just dead. So, from the perspective of my safety I must evaluate the
probability of an accident in terms of my exposure over time, that
being passenger miles.
If we were to take Terrence's argument that the metric it is
aircraft flight hours then it would also be argued that, among
commercial aircraft, the larger the aircraft the less safe it is. Given
that any particular accident would expose more passengers to risk the
you would be wise to fly on carriers with as few passengers as
possible. I believe the raw statistics would run counter to this logic.
Safety must be evaluated in terms of the individual. Consequently the
"event" based evaluation is skewed by the average passenger load of the
compared group. If the average for GA is 2 passengers and the average
for commercial is 50 passengers then the relative ratio between the
two is 25.
I did look up the statistics for 2004 as reported by the NTSB for the
US. I also found this site for a more comprehensive analysis:
http://www.ntsb.gov/Aviation/stats.htm
In 2004, GA had a total of 24 million total flight hours and Commercial (10 seats or more) totaled 23 Million with flight hours (about the same)
GA killed 321 people in airplanes and another 241 on the ground (562
total) and commercial killed 14 passengers and 26 on the ground (40
total) (14 times more for GA). GA had a total of 1,669 accidents and
commercial had 111 (15 times more for GA). It seems that in the US it
is ~15 times safer to fly commercial vs. GA based on flight hours and
perhaps 20 to 50 times that if evaluated by passenger miles.
Remember, with statistics two plus two can be any number you want it to
be, depending on how you define the conditions.
Regards
Brent Regan
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